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How long would a planet that losses its gravity take to break up?

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In my setting, one of the fallouts due to interstellar war between civilisations is that a planet's gravity can be removed. This capability is part of the setting's hyperspace mechanics so the exact details aren't that relevant here. However, in terms of scale, civilisations can affect up to Earth-sized planets. Super-earths, gas giants, and stars will at best end up with localised issues on their surface.

What I'm concerned is with are the consequences to the planet. Obviously any atmosphere, oceans, and loose surface material would quickly get ejected, though the exact shape of the result gas cloud eludes me. Any mountains and other large structures would likely start tearing apart along weak points wouldn't otherwise matter.

But what I really want to know is what happens to the core. Without any gravity, would the core and mantle actually expand and break the crust, leading to a period of increased vulcanism before the planet started cooling? Or would this not actually matter and would an Earth-like planet simply start cooling due to the reduced pressure on the core?

The following assumptions are also relevant

  1. The effect is local. That is, only the mass on the planet at the time of the fallout lacks gravity.
  2. The effect is effectively one way. So a planet isn't going to automatically leave its current orbit. And if a planet has a large moon, like Earth, then the moon will start collecting matter. A gas giant moon system would probably also be interesting, but I am more concerned with Earth-like planets.
  3. The effect isn't strictly zero gravity. It simply isn't reaching as far due to more of it being directed into hyperspace. So it is tapering off faster than the square progression. I assume that the fifth power is sufficient to make gravity have a negligible impact.
  4. Inertia is unchanged. This one is mostly to keep both search & rescue and unscrupulous mining operations somewhat honest. No dragging a planet around with a small tug.
  5. Atomic and molecular physics are otherwise unaffected. This just the necessary handwaving to ensure that lifeforms and electronics on a planet still operate normally, they're just operating under microgravity conditions.
  6. The effect is temporary. Removing a planet from orbit and mucking up the rest of a solar system's orbital mechanics isn't part of the intended effects. Obviously, this particular point has no bearing on any answers.
Why should this post be closed?

This post was sourced from https://worldbuilding.stackexchange.com/q/176050. It is licensed under CC BY-SA 4.0.

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1 answer

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The planet will instantaneously explode.

The Earth has a gravitational binding potential of about $2.25\times10^{32}$ joules, or the weekly energy output of the Sun. This energy also currently being counterbalanced by potential energy of the compression of rock in the earth which prevents the earth collapsing to a point. Without gravity, it will all be released at once since the rock of the earth is no longer being compressed.

Given the energy scales involved, interesting high energy physics will happen before the Earth disappears in a cloud of hot gas. For all intents and purposes that will be instantaneous.

This post was sourced from https://worldbuilding.stackexchange.com/a/176053. It is licensed under CC BY-SA 4.0.

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